Help

 

Here is all the help information you will need about Norcros including FAQ's.

 

 

FAQ's

• Question 1

Can I tile on existing ceramic tiles or do I need to remove the tiles first?

• Question 2

How do I decide if a timber floor is sufficiently rigid and stable to tile on to?

• Question 3

What are the benefits of using Johnson adhesives and grouts with H&R Johnson tiles?

• Question 4

We want to fix large format tiles on to a partition wall – what do we need to consider when carrying out the installation?

• Question 5

Can I fix tiles directly to plaster walls in a shower/wet room?

• Question 6

What are the general recommendations for fixing on to cement-sand screeds with underfloor heating?

Answer 1 

Removing existing tiles can be difficult and time consuming and there is always a risk of damaging the underlying substrate. Tiling onto tile is the preferred route and is acceptable as long as the following guidelines are followed:

 

• Ensure the existing tiles are sound, in good condition, firmly bonded to the background and able to support the weight of the additional tiled finish.
• Remove all loose or hollow sounding tiles and make good.
• Thoroughly clean and de-grease the tiles using a suitable alkaline detergent followed by thorough rinsing with clean water. Allow the tiles to fully dry.

 

New tiles may be fixed using the adhesives recommended in the Norcros & Johnson tick charts on this page.

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Answer 2

The general recommendation is that the floor should not deflect more than 1 in 360. The easiest method of checking the amount of deflection in a timber floor is by the ‘Miniscus Test’. This involves filling a glass to the rim with water and placing it on the floor. Stand at a 1metre distance from the glass and jump on the floor, if the water spills out of the glass then the floor requires strengthening either by overlaying with minimum 12.5mm thick WBP or Marine grade plywood or with a suitable thickness tile backer board, however if there is no spillage the floor may be tiled direct using either Johnson Speed Flex or Norcros Tile Direct to Wood or Tile Direct to Wood Rapid.

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Answer 3

All of the products in the Johnson Professional range have been designed for use with every tile range manufactured by H& R Johnson Tiles Ltd, including ceramic, porcelain, glass and natural stone tiles and mosaics. NBS specifications can be prepared upon request specific to individual projects to include both tiles and adhesives. The use of H&R Johnson tiles with Johnson adhesive systems carries the added benefits of providing the customer with a ‘one stop shop’, i.e. the tiles and adhesive being delivered from the same site, as well as being covered by our unique 10 year product guarantee.

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Answer 4

As with all types of wall tiling, it must be ensured that the substrate is suitable to receive a tile finish and is correct for the type of conditions to which it will be exposed. It must be clean, dry and free from surface contaminants.

 

When fixing large format tiles it is essential to ensure that the background is sufficiently flat to enable good contact to be made between the tile and adhesive, without having to build up the bed of adhesive beneath the tiles. Generally, the maximum recommended thickness for ready mixed adhesives is 3mm, exceeding this thickness could result in the adhesive shrinking and cracking as water is lost during the drying process, weakening the bond strength of the adhesive. Cement-based adhesives are suitable for use up to 6-8mm, although it should be remembered that increasing the adhesive bed thickness will increase the weight which the substrate must support.

 

It must be ensured that the substrate is sufficiently rigid and capable of supporting the weight of tiling. A gypsum plaster finish coat is able to support a maximum weight of 20kg/m2; plasterboard 32kg/m2, tilebacker boards approximately 40kg/m2 (although the board manufacturer should be consulted for their recommendations).

 

It is possible to increase the weight limits of the substrate by fixing anti fracture matting with adhesive to the substrate and mechanically fixing the matting with stainless steel raw bolts and washers at 400mm centres vertically and horizontally through the substrate to the studwork/blockwork behind.

 

Boards should be screw fixed to supporting framework at maximum 300mm centres ensuring that all board edges are fully supported (check with tile backer board manufacturers for their recommendations). When tiling to plasterboard, jointing compound at board junctions should be primed with either Johnson Prime & Seal or Norcros Prime Bond.

 

Large format tiles can be cut in the same manner as smaller format tiles, however a floor tile cutter may be required for thicker gauge tile bodies.

 

When fixing large format tiles with ready mixed dispersion adhesives which dry by water loss, the drying time of the adhesive, especially towards the centre of the tiles, will be increased. This is because of the large surface area of the tiles and the fewer number of joints, through which moisture from the adhesive can escape, than would be present when using smaller format tiles. To prevent grout drying ‘patchy’ due to moisture trapped in the adhesive layer, grouting should be delayed until the adhesive has fully dried.

 

Ready mixed adhesives are suitable for use with tiles up to 300mm x 400mm, however where larger tiles are to be fixed, cement-based adhesives, which dry hydraulically and not by water-loss, should be used. When using cement-based adhesives on to Gypsum plaster/plasterboard, the substrate should be primed with either Johnson Prime & Seal or Norcros Prime Bond to prevent the formation of ettringite resulting from a reaction between the gypsum and cement.

 

Once the adhesive has fully dried, the tiles can be grouted in the usual way.

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Answer 5

Plaster, plasterboard and exterior grade plywood are not generally considered to be suitable for wet areas. In installations subject to occasional wetting however, such as standard domestic shower cubicles or shower heads positioned over a bath where the installation has time to dry out between use, tiles may be fixed directly to these substrates providing that a suitable adhesive and grout are used.

 

It should be noted that the use of ceramic tiles and even a waterproof grout can not be guaranteed to totally eliminate the ingress of water to the underlying substrate. Minor defects in workmanship and movement in the structure can result in fissures through which water can pass. The application of a liquid applied tanking membrane such as Johnson Waterproofing Membrane or Norcros Wet Seal prior to tiling will prevent the passage of water.

 

In power showers and more frequently used installations the application of a tanking membrane to these substrates is considered to be essential.

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Answer 6

The screed should be a minimum of 3 weeks old before the heating is brought to its intended operating temperature and maintained at that temperature for a minimum of 3 days. It should then be allowed to cool to room temperature before ceramic tiles or natural stone are fixed.

 

Tiles should be fixed in a highly polymer modified cement-based adhesive and grouted with either a ‘flexible’ CG2 grout or a CG1 grout with the addition of a flexible additive (refer to tick charts).

 

The heating may be switched on 14 days after completion of tiling, raising the temperature gradually at a rate of 5oC per day.

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